The influence of ocular dominance on monovision--the interaction between binocular visual functions and the state of dominant eye's correction

PURPOSE: To examine the interaction between binocular visual functions and the correction of the dominant eye, i.e., for far vs. near vision in monovision. SUBJECTS AND METHODS: Ten healthy subjects without any ophthalmological disease were examined. After cycloplegia, the eyes of the subjects were corrected by soft contact lenses (difference in lens power between the lenses: 2.5 D) with an artificial pupil(diameter: 3.0 mm). Visual acuity at various distances, contrast sensitivity, and near stereoacuity were measured while the dominant eye determined by the hole-in-card test (sighting dominance) was corrected for far and near vision. RESULTS: Binocular visual acuity was better than 1.0(20/20) at all distances. When the dominant eye was corrected for distance, the binocular visual acuity at 0.7 m was better than the monocular visual acuity; contrast sensitivity was better within the spatial frequency range of 0.5-4.0 cycles per degree, and near stereoacuity by Titmus stereo tests improved. CONCLUSION: These results suggest that dominant eyes should be corrected for far vision for better binocular summation at middle distances, and near stereoacuity.     

The effect of monovision contact lens wear on driving performance

Background : A number of studies have highlighted the problems with driving reported by wearers of monovision contact lens corrections. In this study, we wished to investigate this further, by determining whether driving performance as measured on the open road under daytime conditions is worse when drivers wear their monovision contact lenses compared to their habitual correction. Methods : Thirteen subjects with healthy eyes and corrected visual acuity of 6/6 were selected. Each had worn monovision contact lenses for at least three months. All subjects had their driving performance assessed while driving their own vehicles on an open road course, with both monovision contact lenses and their other habitual correction (spectacles or unaided). Results : No statistically significant differences were found in driving performance when subjects wore their monovision contact lenses compared to when they wore their habitual distance correction. Conclusions : The results indicate that monovision does not adversely affect driving performance in daylight hours for adapted wearers. However, limitations in the study design are acknowledged, including the relatively small sample size, lack of standardisation of the habitual correction and the use of adapted wearers. Future studies are recommended to investigate these issues further.     

The influence of ocular dominance on monovision--the influence of strength of ocular dominance on visual functions

PURPOSE: Monovision is a method of correction for presbyopia. We have reported the advantage of conventional monovision (the dominant eye is corrected for distance). In this study, we investigated the influence of interocular imbalance of dominancy on the visual function. SUBJECTS AND METHODS: Ten healthy subjects without any ophthalmologic disease participated. After cycloplegia, the eyes of the subjects were corrected by soft contact lenses with an artificial pupil (diameter: 3.0mm). The dominant eye was corrected for distance, and the difference in lens power between the lenses was 2.5 D. The subjects were classified into two groups by strength of the imbalance of sensory dominance, which was determined by using binocular rivalry. Binocular visual functions (visual acuity at various distances, contrast sensitivity, near stereoacuity) were compared between the two groups. RESULTS: Subjects with strong imbalance of sensory dominance showed decreased near visual acuity as well as decreased binocular summation of contrast sensitivity at low spatial frequencies. On the other hand, near stereoacuity was not affected by the imbalance of sensory dominance. CONCLUSION: These results suggest that strong imbalance of sensory dominance interferes with binocular visual functions in monovision. Thus, the evaluation of ocular dominance is crucial for clinical applications of monovision.     

Monovision: a review

In presbyopia, patients can no longer obtain clear vision at distance and near. Monovision is a method of correcting presbyopia where one eye is focussed for distance vision and the other for near. Monovision is a fairly common method of correcting presbyopia with contact lenses and has received renewed interest with the increase in refractive surgery. The present paper is a review of the literature on monovision. The success rate of monovision in adapted contact lens wearers is 59-67%. The main limitations are problems with suppressing the blurred image when driving at night and the need for a third focal length, for example with computer screens at intermediate distances. Stereopsis is impaired in monovision, but most patients do not seem to notice this. These limitations highlight the need to take account of occupational factors. Monovision could cause a binocular vision anomaly to decompensate, so the pre-fitting screening should include an assessment of orthoptic function. Various methods have been used to determine which eye should be given the distance vision contact lens and the literature on tests of ocular dominance is reviewed. It is concluded that tests of blur suppression are most likely to be relevant, but that ocular dominance is not fixed but is rather a fluid, adaptive, phenomenon in most patients. Suitable patients can often be given trial lenses that allow them to experiment with monovision in real world situations and this can be a useful way of revealing the preferred eye for each distance. Of course, no patient should drive or operate machinery until successfully adapted to monovision. Surgically induced monovision is less easily reversed than contact lens-induced monovision, and is only appropriate after a successful trial of monovision with contact lenses.     

Contrast sensitivity with contact lens corrections for presbyopia

We measured contrast sensitivity at three distances (330 mm, 660 mm and 4 m) with six contact lens and two multifocal spectacle corrections for presbyopia. The two spectacle corrections were D-segment bifocals and trifocals and the contact lens corrections were distance contact lens with lookover spectacles, soft progressive bifocals, soft concentric bifocals, monovision, modified monovision, and hard crescent segment bifocals. The spectacle corrections in general gave better results for the contrast sensitivity function (CSF), than did the contact lens corrections. Distance contact lenses with lookover spectacles performed best of the contact lens corrections used. However, the differences in CSF between the various contact lens corrections were small and not statistically significant.     

Interest of presbyopes in contact lens correction and their success with monovision.

The presbyopic population is seen as a large potential source of contact lens wearers. The aims of this study were: (1) to estimate the percentage of presbyopes interested in contact lenses, (2) to ascertain the success of interested presbyopes with monovision correction, and (3) to determine the percentage willing to continue wearing monovision lenses after 1 month's trial. Seven practitioners in Sydney surveyed consecutive presbyopes attending their practices about their interest in contact lenses. Of the 1133 presbyopes surveyed, 314 (28%) were interested in trying monovision lenses. A total of 72 patients were subsequently fitted with monovision in high water content hydrogel form. After 1 month, 46 of these patients (64%) were still wearing the lenses, and 39 (54%) expressed willingness to continue with monovision correction. The major reasons for discontinuation from lens wear during the 1-month trial were inadequate vision and difficulty in lens handling.     

Comparison of multifocal and monovision soft contact lens corrections in patients with low-astigmatic presbyopia.

PURPOSE: The purpose of this study was to assess visual performance and patient satisfaction with two presbyopic soft contact lens modalities. METHODS: A crossover study of 38 patients with presbyopia was conducted. Patients were randomized first into either multifocal (Bausch & Lomb SofLens Multifocal) or monovision (SofLens 59) for 1 month. Visual performance was measured with high- and low-contrast visual acuity at distance and near and near stereoacuity. Patients' satisfaction was measured by the National Eye Institute Refractive Error Quality of Life Instrument questionnaire and by recording the patient's final lens preference. RESULTS: Patients maintained at least 20/20 binocular vision with both multifocal (MF) and monovision (MV) contact lenses under high-contrast conditions at distance and near. Under low-contrast conditions, patients lost less than a line of vision from the best spectacle correction to either multifocal or monovision contact lens correction at distance (pMF = 0.001, pMV = 0.006). Under low-contrast conditions at near, multifocal wearers lost five to six letters and monovision wearers lost two letters of vision (pMF < 0.001, pMV = 0.03, pMF/MV = 0.005). The average stereoacuity decreased by 79 s arc with monovision vs. multifocal contact lenses (p = 0.002). On the NEI-RQL, patients reported worse clarity of vision (pMF = 0.01, pMV < 0.001), more symptoms (pMF = 0.09, pMV = 0.01), and an improvement in their appearance with contact lens wear (pMF < 0.001, pMV < 0.001). Seventy-six percent of patients reported that they preferred multifocal contact lenses, and 24% preferred monovision contact lenses (p = 0.001). CONCLUSION: The majority of our patients preferred multifocals to monovision, most likely because the Bausch & Lomb SofLens Multifocal provides excellent visual acuity without compromising stereoacuity to the same degree as monovision.     

The holographic/diffractive bifocal contact lens

Presently, practitioners are somewhat limited in the available options for correction of presbyopia with contact lenses. Neither the form of contact lens design (segmented, aspheric, or concentric) or fitting scheme (such as monovision) have high enough success to dominate the market. To meet this growing demand, a new holographic/diffractive bifocal contact lens is being introduced by several manufacturers^1,2,3,4,5. Although different lens materials and slightly modified designs have been proposed, these lenses all form images based upon a similar concept. This paper attempts to simplify the principles behind “how the holographic bifocal contact lens works.” This will include a review of diffraction and refraction as well as the application of these concepts in the diffractive lens design. Comparisons between the holographic and conventional bifocal contact lenses along with advantages and disadvantages will also be presented.     

Peripheral visual acuity with monovision and other contact lens corrections for presbyopia

We have conducted two experiments to investigate the effect of monovision and other contact lens corrections for presbyopia upon peripheral visual acuity. In the first study, we measured binocular peripheral visual acuity using Landolt rings with seven subjects wearing a monovision correction. The Landolt rings were presented at eccentricities of 10, 20, 40, and 70 degrees on each side of the subject, with near additions of +1.50 D, +2.50 D, and no addition. We found no significant effect of monovision correction on peripheral visual acuity. In the second experiment we measured the peripheral visual acuity of 11 presbyopic subjects wearing distance contact lenses with lookover spectacles, soft progressive bifocal contact lenses, soft concentric bifocal contact lenses, monovision contact lenses, modified monovision contact lenses, and hard bifocal contact lenses using Koenig bar targets. There were no significant differences in peripheral visual acuity between any of the contact lens corrections for presbyopia.     

Monovision for treatment of accommodative esotropia with a high AC/A ratio.

PURPOSE: The purpose of this study was to determine whether monovision will successfully reduce the near esodeviation in patients with high AC/A ratio accommodative esotropia. METHODS: The records of all patients who wore monovision contact lenses for at least 3 months were retrospectively reviewed to determine baseline patient characteristics, long-term motor alignment, sensory status, and patient convenience. RESULTS:TEN patients 10 to 28 years of age wore monovision contact lenses for a mean of 28.7 months to date. All patients maintained an esodeviation of < or = 10 prism diopters at distance and near, except 1 patient whose near esodeviation increased over time. Of the 5 patients for whom data were available, 1 experienced a significant decrease in stereoacuity. No patients discontinued monovision because of visual symptoms; however, 1 did so because of the inconvenience of contact lens care. No serious ocular side effects from contact lens wear were noted in the study. CONCLUSION: Use of monovision contact lenses is a safe and effective method of reducing near-angle esodeviation associated with nonrefractive high AC/A ratio accommodative esotropia. Many patients are willing to accept the visual compromises inherent in monovision to eliminate wearing bifocal spectacles.     

Presbyopic fitting strategies: Fitting lenses to patients,not patients to lenses

Eighty-six presbyopic patients who were interested in contact lens wear but had no history of using contact lenses for the correction of presbyopia were entered into a study performed across five independent contact lens practices. Patients were fit utilizing a fitting strategy flowchart that included monovision, diffractive, and aspheric simultaneous and alternating vision presbyopic corrections. At the conclusion of the study, 83% of the patients were successful utilizing the criterion that the patient was still actively wearing the lenses. Fifty-two percent were fit with monovision, 14% were fit in alternating vision lenses, while 6% and 10% were fit with aspheric and diffractive lenses, respectively, including modified monovision.     

Ocular dominance and the interocular suppression of blur in monovision

Presbyopic contact lens patients with monocular corrections (monovision) see clearly at all distances by virtue of an interocular suppression of anisometropic blur that occurs regionally between corresponding retinal areas. This suppression fails to occur with small high-contrast targets viewed under low luminance conditions. The effect of target size and contrast upon interocular suppression of blur was quantified by reducing contrast of a bright test spot, viewed binocularly while wearing various plus lenses monocularly, until the out-of-focus image was suppressed. The strength of interocular suppression was equivalent when the plus lens was before either eye. However, after subjects wore a plus lens over their nonsighting eye for one day, interocular suppression of blur became enhanced when the nonsighting eye was blurred, and it became reduced when the sighting eye was blurred. Successful monovision subjects suppressed blur at higher contrast levels than did unsuccessful subjects. These results suggest a possible clinical test for quantifying adaptation to monovision.     

A market survey of contact lens practice in Hong Kong

Purpose : The aim of this survey was to evaluate the use of contact lenses, current prescribing habits of practitioners and the development of the contact lens market in Hong Kong. Methods : Questionnaires were sent to all registered contact lens practitioners in Hong Kong. This questionnaire sought information about their choices on prescribing contact lenses and lens care products and their opinions on continuing education and future trends of contact lens development. Results : A total of 286 responses (22 per cent) were returned. On average, the respondents reported that 36 per cent of their patients were contact lens wearers and most were myopes. The ratio of new fittings to refittings was 1:3. Of the contact lens wearers, 66 per cent were fitted with planned replacement lenses, mostly daily disposable lenses. Multipurpose solution was the most popular lens care regimen prescribed. Only 48 per cent of astigmatic patients were fitted with toric lenses and the use of overnight orthokeratology and silicone hydrogel lenses was limited. Single vision contact lenses with over‐spectacles and monovision contact lenses were the most popular management for presbyopes. Dryness was the major problem reported by contact lens wearers. Practitioners look forward to further development of custom‐made toric, multifocal and silicone hydrogel lenses. The major source of new contact lens information was communication with contact lens suppliers. Conclusion : Compared to previous reports, there was no significant change in the prescribing habits of practitioners. The major complaint of contact lens wearers is still ocular dryness. The contact lens market is driven by younger contact lens wearers, and planned replacement soft contact lenses together with multipurpose solutions dominate. The use of bifocal/multifocal lenses remained low and practitioners want low cost bifocal/multifocal contact lenses with better visual performance and toric lenses with a wider range in parameters. The use of overnight wear lenses such as silicone hydrogel and ortho‐k lenses is limited and 30 days continuous wear silicone hydrogel lenses are prescribed mainly for daily wear.     

Bifocal hydrogel lenses: an overview

Until the advent of bifocal hydrogel lenses, monovision or reading glasses were the modes of correction for hydrogel contact lens wearing presbyopes. Recent design innovations and improvements in the manufacturing technology of soft contact lenses have made possible new developments in bifocal hydrogel lenses. Patient selection and patient education play key roles in optimizing patient success. There are several hydrogel bifocal designs that are possible for the presbyope. The variations of these designs and their pertinent considerations are discussed.     

Surgical monovision and monovision reversal in LASIK

PURPOSE: This study was designed to assess the success of surgical monovision in presbyopic patients. METHODS: A university refractive surgery center retrospective chart review of 82 patients who elected to undergo surgical monovision with laser in situ keratomileusis (LASIK) between January 2000 and January 2003 was conducted. Specific factors included for analysis included preoperative and postoperative defocus spherical equivalent, whether the patient underwent enhancements, whether the patient underwent a preoperative monovision trial with contact lens, and whether the patient underwent monovision reversal. RESULTS: Eighty-two patients who underwent LASIK for monovision were analyzed. Mean preoperative spherical equivalent in the distance-corrected eye was -4.07 (standard deviation (SD), 2.49); for the eye corrected for near vision, mean preoperative spherical equivalent was -4.10 (SD, 2.56). Postoperative spherical equivalent in the distance eyes was -0.01 (SD, 0.38) and in the near eyes -1.24 (SD, 0.91). There were 6 enhancements in the near eyes (7%) and 17 enhancements in the distance vision eyes (21%). This difference was statistically significant (P = 0.007). Thirty patients underwent a contact lens trial of monovision before LASIK, and none of those patients elected monovision reversal. There were 52 patients who did not undergo a contact lens monovision trial before LASIK monovision, and 2 of these patients underwent monovision reversal. Monovision success in this population was 97.6%. CONCLUSION: Surgical monovision can help presbyopic patients achieve their goal of reduced dependence on spectacles. A trial of monovision contact lenses or spectacles may be important in helping surgeons select patients for successful surgical monovision.     

An international survey of contact lens prescribing for presbyopia

Purpose: The aim was to determine world‐wide patterns of fitting contact lenses for the correction of presbyopia. Methods: Up to 1,000 survey forms were sent to contact lens fitters in each of 38 countries between January and March every year over five consecutive years (2005 to 2009). Practitioners were asked to record data relating to the first 10 contact lens fittings or refittings performed after receiving the survey form. Results: Data were received relating to 16,680 presbyopic (age 45 years or older) and 84,202 pre‐presbyopic (15 to 44 years) contact lens wearers. Females are over‐represented in presbyopic versus pre‐presbyopic groups, possibly reflecting a stronger desire for the cosmetic benefits of contact lenses among older women. The extent to which multifocal and monovision lenses are prescribed for presbyopes varies considerably among nations, ranging from 79 per cent of all soft lenses in Portugal to zero in Singapore. There appears to be significant under‐prescribing of contact lenses for the correction of presbyopia, although for those who do receive such corrections, three times more multifocal lenses are fitted compared with monovision fittings. Presbyopic corrections are most frequently prescribed for full‐time wear and monthly replacement. Conclusions: Despite apparent improvements in multifocal design and an increase in available multifocal options in recent years, practitioners are still under‐prescribing with respect to the provision of appropriate contact lenses for the correction of presbyopia. Training of contact lens practitioners in presbyopic contact lens fitting should be accelerated and clinical and laboratory research in this field should be intensified to enhance the prospects of meeting the needs of presbyopic contact lens wearers more fully.     

Neuroadaptation of presbyopia-correcting intraocular lenses

PURPOSE OF REVIEW: Advances in the design of intraocular lenses give options to patients for some return to the optical accommodation needed to focus on objects at different distances. Technology is only improving these options for presbyopic-correcting intraocular lenses. Surgeons must consider the possible neuroadaptation abilities in patients that may help in the success of using these lenses. RECENT FINDINGS: The hierarchy of the visual system allows two disparate retinal images to combine to form a single picture with depth. Attempts to correct presbyopia with intraocular lenses add complexity to the pathway with the possible introduction of monovision or intraocular rivalry. The neuroadaptation involved in successful use of these lenses has not been study but has been well established in other neurologic processing. SUMMARY: Understanding what patient selection factors are important for neuroadaptation may contribute to outcome success.     

Accommodating intraocular lenses

PURPOSE OF REVIEW: With the advent of interest in accommodative lenses as a solution for presbyopia and the growing baby-boomer demographic, ophthalmic surgeons will have the opportunity to provide this technology to facilitate near, intermediate, and distance vision for their patients. RECENT FINDINGS: At present, six corporate entities and lens designs are attempting to commercialize accommodative intraocular lens devices. One Food and Drug Administration (FDA) clinical trial has been completed and the first FDA-approved accommodating lens is available. SUMMARY: For the first time, ophthalmic surgeons will be able to provide a full range of visual focus in each eye of a patient to maintain binocular function while also avoiding the unwanted mesopic and scotopic visual disturbances that are experienced with monovision and multifocal lens technologies. Accommodative intraocular lenses could revolutionize not only cataract visual rehabilitation but also the surgical approach to presbyopia.